I use a vacuum sealer and *gasp* a refrigerator (not freezer). I just don't have room in my freezer for several pounds of leaf hops.... but I do between my kegs in the keezer. According to BeerSmith's Hop Age tool, the difference between fridge and freezer for 6 months is about 0.3% AA (assuming vacuum sealed).

I did a brew day at a local brewery about a month back, and they used two chest freezers to store all their hops. After pulling hops for the brew, they purge the bags with nitrogen and seal it back up.

So, if you don't want to buy a nitrogen tank, just get your hands on some liquid nitrogen.